675
International Journal of Scientific Engineering and Technology Volume No.3 Issue No.5, pp : 675-679
(ISSN : 2277-1581) 1 May 2014
Numerical Study on the Effect of Ratio among Various of Submersion on Three Dimensional Velocity Components around T-shaped Spur Dike Located in a 90 Degree Bend M. Vaghefi1*, M. Shakerdargah2, M. Akbari3 1,3 2
Department of Civil Engineering, Persian Gulf University, Bushehr, Iran. Department of Civil Engineering, Islamic Azad University, Bushehr, Iran Corresponding Author Email: vaghefi@pgu.ac.ir
Abstract: Spur dike is one of the hydraulic structures used in rivers to protect river banks. In this paper, flow pattern around a T-shaped spur dike which is located in a 90◦ bend and different amounts of submersion has been studied using Flow-3D. Numerical results have been compared with experimental results and have been analysed.
Keywords: Submerged T-shaped Spur Dike, Three Dimensional Velocity, Flow Pattern, 90 Degree Bend, Flow3D
I. Introduction Since long time ago, rivers have been considered one of the most basic sources of water for human civilization. Despite the vital role they play for human life, they have also been one of the natural enemies of human beings. Rivers have gone through changes in their life cycle, and erosion of outer walls and river beds, and sedimentation in inner walls are some instances which cause irreparable damage to inhabitants and constructions by the rivers. Spur dikes are extended in rivers in a vertical or angular position in proportion to river walls. These structures protect river walls from erosion by redirecting the flow from the walls to the middle of the channel. Spur dikes change flow field, and cause a strongly turbulent three-dimensional flow. Horseshoe vortexes downstream the separation are formed because of a lot of pressure behind the structure, and the flow near the bed, and the flow down the upstream of the structure [i]. Gill in 1972, did an experimental study showing that the distance between the spur dikes is very much dependent on the radius of curvature [ii]. Rajaratnam & Nwachukwu studied the turbulent flow near groin in 1983. Based on experimental observations, the deflected flow has been analysed using the model of the three‐dimensional turbulent boundary layer [iii]. Kong and Platfoot in 1996, investigated the effect of channel geometry and operational parameters on the flow pattern in a two dimensional model [iv]. Graf and Blanckaert in 2001, did an experimental study on a 120º bend channel and measured secondary flow and maximum velocity at the 60º cross section [v]. McCoy et al. in 2004, Investigated flow pattern around and between two spur dikes using LES method in an open channel [vi]. Fazli et al. in 2008, did an experimental study on a 90 degree bend channel to study the parameters affecting scour around straight spur dikes [vii]. Ghodsian and Vaghefi in 2009, carried out an experimental study on how changes in Froude Number, and length of wing and web of T-shaped spur dike affect flow pattern in a 90 degree bend [viii]. Duan in 2009, investigated average and turbulent flow around a straight spur dike located in an experimental channel with rigid bed [ix].
IJSET@2014
Since 2008, Vaghefi et al. have experimentally investigated flow pattern and scour around unsubmerged T-shaped spur dike in a 90 degree bend in different parameters including Froude number, curvature radius, spur dike position, spur dike geometry, time effect, flow conditions etc. [x-xii]. Acharya et al. in 2013, carried out a three-dimensional numerical investigation of turbulent flow pattern around series of straight spur dikes located in a straight route, using Flow-3D [xiii]. Since there has not been enough study on flow pattern around submerged spur dikes located in bend, in this study, the effect of submersion on flow pattern around T-shaped spur dike located in a 90 degree bend has been numerically investigated. Also, the results from numerical modelling have been compared with those from experimental model.
II. Material and Methodology
Experimental Model Introduction
The intended experiments have been carried out by Vaghefi [x] in Hydraulics laboratory of Tarbiat Modares University in Iran, on a laboratory flume with the width of 60 cm, and the height of 70 cm, in a compound of straight and bend route. The straight upstream route is 710 cm long, and is connected to straight downstream route of 520 cm long via a 90 degree bend with an external radius of 270 cm, and an internal radius of 210 cm. The ratio of bend radius to width of channel is 4. Uniform sediments have an average diameter of 1.28 mm. Also the flow discharge equals to 25 lit/s. The spur dike used in this experiment is a T-shaped spur dike. The length of wing (L) and that of web (l) are equal to 9 cm, with the height of 25 cm. This spur dike is vertical and unsubmerged in a 45 degree position. The features of the laboratory flume and schematic view of the T-shaped spur dike is presented in Figure (1).
Figure (1): features of the laboratory flume and schematic view of T-shaped spur dike
Page 675